Since the earliest days of mankind plants have been used as sources of pharmacologically active materials. One such plant is Cannabis sativa, colloquially known as marijuana, which contains such pharmacologically-active substances as Δ9-tetrahydrocannabinol and other cannabinoids, which historically were ingested by smoking dried leaves of Cannabis sativa. 
For medical and cosmetic purposes use of crude plant material poses a number of problems. First, it renders the dosage unknown and potentially highly variable. Second, the pharmacologically-active material may well constitute only a small proportion of the plant in question. Third, the desired pharmacologically-active material may well be admixed with toxic or otherwise undesirable adulterants. For this reason, it is often desirable to extract the desired pharmacologically-active material from its biological source. Such considerations prompted, e.g., the extraction of salicylic acid from willow bark in the mid-eighteenth century, and to the extraction of taxol from the bark of the Pacific yew tree in the mid-twentieth century
U.S. Pat. No. 6,730,519 to Elsohly and Ross discloses a method of extraction involving use of non-polar solvents and purification by column chromatography on alumina columns.
US20030017216, filed by Schmidt and Coco, discloses an extraction method that uses various organic solvents but with a curtailed extraction period to extract primarily the surface structures of the plant.
U.S. Pat. No. 7,622,140 to Whittle et al. discloses an extraction method that uses hot air to volatilize cannabinoids.
U.S. Pat. No. 7,344,736 to Whittle et al. discloses an extraction method that uses sub-critical CO2 to extract cannabinoids from Cannabis plant material, while US20040049059, filed by Mueller and Mueller, discloses a supercritical CO2 extraction method, as does. Similarly,
US20080103193, filed by Castor et al., discloses use of super- or near-critical carbon dioxide, nitrous oxide, ethylene, ethane, propane and chlorodifluoromethane, with or without organic co-solvents, as extractants for Cannabis plant material.
US20110256245, filed by Rosenblatt et al., discloses an extraction method for Cannabis flower trimmings with trichomes (glandular hairlike appendages) involving covering the trimmings with cold water.
US20120264818, filed by Newland, discloses extraction of Cannabis plant material with dimethylsulfoxide, and the use of the resulting extract as a topically applied composition for the treatment of various skin ailments such as dermatitis.
U.S. Pat. No. 8,343,553, to Hospodor, discloses a device for preparing extracts of Cannabis plant material, as does US2013/0251824, filed by Hospodor and Rapp.
US2013/0079531, filed by Barringer, discloses a process for rapid extraction of Cannabis plant material through brief contact with an organic solvent below room temperature to minimize the extraction of non-cannabinoid contaminants.
U.S. Pat. No. 8,337,908, to Letzel et al., discloses use of Cannabis extracts for, inter alia, topical use in treatment of various skin ailments, such extracts being prepared by a variety of known extraction methods and extractants.
U.S. Pat. No. 8,603,515, to Whittle, discloses pharmaceutical formulations of cannabinoids for administration via a pump action spray.
U.S. Pat. No. 8,512,767 to Ross discloses Cannabis-derived compositions suitable for sublingual aerosol or spray delivery.
US2008/0119544, filed by Guy and Pertwee, discloses various therapeutic uses of cannabinoid extracts, as does US2008/0139667, filed by Robson and Guy. US2010/0249223, filed by Di Marzo et al., discloses the therapeutic and prophylactic use of cannabinoid extracts in connection with, inter alia, cancer of the skin.
U.S. Pat. No. 8,524,286, to Smothers, discloses use of aloe to extract cardiac glycosides from Nerium oleander. 
Each of the references above is hereby incorporated by reference in its entirety.
While the possession or use of Cannabis has been illegal in the United States since 1937, the medicinal properties of cannabinoids (e.g., for treatment of glaucoma) have become increasingly appreciated, which has spurred efforts to facilitate the legal and controlled medical use of cannabinoids. Extraction of cannabinoids and tetrahydrocannabinol from Cannabis plant material facilitates their use clinically by allowing administration of compositions of known and/or predetermined potency and purity. Accordingly, a need exists for a way to effectively extract pharmacologically-active compounds from plants of the genus Cannabis, and in particular using an extractant which itself is cosmetically acceptable or beneficial.